In chemical vapor deposition (CVD) and related vapor deposition techniques, such as atomic layer deposition (ALD), liquid or solid source chemicals are often used. Many of those chemicals react aggressively with moisture and/or oxygen. In order to preserve the purity and volatility of these source chemicals, the container in which they are stored should be vacuum tight to a high degree, compatible with ultra high vacuum (UHV) conditions. It is convenient to use a metal container, which can easily be made UHV compatible and is not susceptible to breakage.
However, the container should also comprise a sealable opening to load the chemical into the container or to remove used material from the container. For this purpose such containers are provided with a removable closure. A polymer O-ring typically cannot be used to seal the removable closure against the container because it is not UHV compatible. Another problem related to the use of polymer O-rings is that polymer O-rings slowly deteriorate in contact with many of the chemicals used in such containers. Furthermore, some of the source materials have such a low vapor pressure that the container has to be heated to a high temperature in order to increase the vapor pressure. Such high temperatures are also harmful to polymer O-rings.
For these reasons, metal seals are the more appropriate to seal the lid against the container and to seal other connections to the container. In such a seal, a metal sealing gasket is sandwiched between two metal flanges. The flanges are made of a hard construction metal, such as stainless steel, and the metal gasket is made of a ductile metal. By pressing the two flanges together, with the sealing gasket therebetween, a high quality seal is formed. However, the two most widely used metals for metals seals, namely aluminum and copper, are also susceptible to attack by many of the source chemicals. Accordingly, a more chemically resistant material, such as nickel, is preferably employed. One disadvantage of nickel is that it is harder and less ductile than aluminum and copper, such that a nickel gasket requires a higher compressive force to maintain the vacuum integrity of the seal.
As shown for the container 10 of FIG. 1, the force for compressing metal gaskets against the container flanges is typically exerted by a large number of nuts 12 and bolts 14, evenly distributed along the circumference of flanges 16, 18, with each bolt sticking through a hole through both flanges 16, 18. When the container 10 needs to be opened or closed a large number of nuts 12 and bolts 14 need to be released or tightened, respectively. This is rather cumbersome, particularly when recharging or discharging the container is performed in a nitrogen purged glove box to avoid exposure of the chemicals to ambient air.
It is accordingly an objective of the present invention to avoid these and other disadvantages and to provide in a vacuum tight metal source container for chemicals used in vapor deposition processes. The container should allow easy, convenient and reliable recharging and discharging.